Four-Component Bicyclization Approaches to Skeletally Diverse Pyrazolo[3,4-b]pyridine Derivatives

Abstract

A novel four-component bicyclization strategy has been established, allowing a flexible and practical approach to 37 examples of multicyclic pyrazolo[3,4-b]pyridines from low-cost and readily accessible arylglyoxals, pyrazol-5-amines, aromatic amines, 4-hydroxy-6-methyl-2H-pyran-2-one, and cyclohexane-1,3-diones. The polysubstituted cyclopenta[d]pyrazolo[3,4-b]pyridines were stereoselectively synthesized through a microwave-assisted special [3+2+1]/[3+2] bicyclization with good control of the spatial configuration of exocyclic double bonds. The novel [3+2+1]/[2+2+1] bicyclization resulted in 17 examples of unreported pyrazolo[3,4-b]pyrrolo[4,3,2-de]quinolones. Reasonable mechanisms for forming two new types of multicyclic pyrazolo[3,4-b]pyridines are also proposed.

Exploration of pyrazole based aldo‐x bifunctional building blocks for the synthesis of pyrazole annulated molecular architectures

“…[ 13 ] Additionally, they act as liquid crystals, [ 14 ] semiconductors, [ 15 ] and organic light‐emitting diodes. [ 16 ] Pyrazole and its analogs have also received considerable attention because of their synthetic application as chiral auxiliaries, [ 17 ] reagents in various multicomponent reactions, [ 18 ] and guanylating agents. [ 19 ] From the literature survey, it has also revealed that substituted pyrazoles are also utilized as chelating agents for the detoxification of undesired metal ions.…”

Multicomponent Reactions of Arylglyoxal, 4‐Hydroxycoumarin, and Cyclic 1,3‐C,N‐Binucleophiles: Binucleophile‐Directed Synthesis of Fused Five‐ and Six‐Membered N‐Heterocycles

“…[34] Similarly, the four-component reaction of arylglyoxal, aminopyrazole, aromatic amine, and dimedone/4-hydroxy-6-methyl-2-pyrone provide either tetracyclic or tricyclic fused heterocycles (Scheme 1, Equation 4). [35] Considerable attention has been paid in recent times to the development of new multicomponent reactions (MCRs) with arylglyoxals because of their interesting reaction behavior. [36][37][38][39][40] After a literature survey on the interesting reactivity patterns of arylglyoxals with aminopyrazoles, and in continuation of our…”

Aldo‐X Bifunctional Building Blocks for the Synthesis of Heterocycles

“…Tu et al. reported the four‐component reaction of phenylglyoxal, 7 , 4‐hydroxy‐6‐methyl‐2 H ‐pyran‐2‐one 9 , and aniline, which could be used to synthesize multicyclic pyrazolo[3,4‐ b ]pyridine 10 (Scheme ) . The authors proposed a mechanism in which the initial event of the reaction was the condensation of 9 and aniline.…”